 @media all and (max-width: 400px) {
	

  ;

  (function (designWidth, maxWidth) {

    var doc = document,

      win = window,

      docEl = doc.documentElement,

      remStyle = document.createElement("style"),

      tid;



    function refreshRem() {

      var width = docEl.getBoundingClientRect().width;

      maxWidth = maxWidth || 540;

      width > maxWidth && (width = maxWidth);

      var rem = width * 100 / designWidth;

      remStyle.innerHTML = 'html{font-size:' + rem + 'px;}';

    }



    if (docEl.firstElementChild) {

      docEl.firstElementChild.appendChild(remStyle);

    } else {

      var wrap = doc.createElement("div");

      wrap.appendChild(remStyle);

      doc.write(wrap.innerHTML);

      wrap = null;

    }

    //要等 wiewport 设置好后才能执行 refreshRem，不然 refreshRem 会执行2次；

    refreshRem();



    win.addEventListener("resize", function () {

      clearTimeout(tid); //防止执行两次

      tid = setTimeout(refreshRem, 300);

    }, false);



    win.addEventListener("pageshow", function (e) {

      if (e.persisted) { // 浏览器后退的时候重新计算

        clearTimeout(tid);

        tid = setTimeout(refreshRem, 300);

      }

    }, false);



    if (doc.readyState === "complete") {

      doc.body.style.fontSize = "16px";

    } else {

      doc.addEventListener("DOMContentLoaded", function (e) {

        doc.body.style.fontSize = "16px";

      }, false);

    }

  })(400, 700);





}